From 86070c1931554cd30146ae7de94433bdb0f0804c Mon Sep 17 00:00:00 2001
From: Karl Williamson <khw@cpan.org>
Date: Fri, 3 Nov 2023 12:45:11 -0600
Subject: [PATCH] Experimentally enable per-thread locale emulation

This is set to end in 5.39.10, but will give us field experience in the
meantime.
---
 locale.c   | 8 +++++---
 makedef.pl | 6 +++++-
 perl.h     | 2 ++
 3 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/locale.c b/locale.c
index 21a0cc930e09..8242a4e62435 100644
--- a/locale.c
+++ b/locale.c
@@ -133,9 +133,11 @@
  *    expects.  The perl core has made those changes, so pure perl programs
  *    become thread-safe.  Well-behaved XS code also keeps things thread-safe,
  *    either by not using locale-dependent system calls, or by changing to use
- *    the wrapper macros.  This layer is not chosen if the platform has native
- *    thread-safe locale handling.  Also, currently perl must have been
- *    Configured with "-Accflags=-DEMULATE_THREAD_SAFE_LOCALES".
+ *    the wrapper macros.  This layer is chosen on threaded perls where the
+ *    platform doesn't have working native thread-safe locale handling, and
+ *    there is no manual override in Configure.  To turn if off add these to
+ *    the Configuration options:
+        -Accflags='-DNO_THREAD_SAFE_LOCALE'" -Accflags='-DNO_POSIX_2008_LOCALE'"
  *
  *    This implementation is based on the observation that the underlying
  *    locale matters only to relatively few libc calls, and only during their
diff --git a/makedef.pl b/makedef.pl
index 2d2c8c613c04..2db1a03ce366 100644
--- a/makedef.pl
+++ b/makedef.pl
@@ -181,6 +181,9 @@ BEGIN
     {
         $define{USE_THREAD_SAFE_LOCALE} = 1;
     }
+    else {
+        $define{EMULATE_THREAD_SAFE_LOCALES} = 1;
+    }
 }
 
 if ($define{USE_POSIX_2008_LOCALE} && $define{HAS_QUERYLOCALE})
@@ -190,7 +193,8 @@ BEGIN
     # Don't need glibc only code from perl.h
 }
 
-if ($define{USE_POSIX_2008_LOCALE} && ! $define{USE_QUERYLOCALE})
+if (  ($define{USE_POSIX_2008_LOCALE} && ! $define{USE_QUERYLOCALE})
+    || $define{EMULATE_THREAD_SAFE_LOCALES})
 {
     $define{USE_PL_CURLOCALES} = 1;
 }
diff --git a/perl.h b/perl.h
index d1aac447387b..62bbc12f2b76 100644
--- a/perl.h
+++ b/perl.h
@@ -1251,6 +1251,8 @@ typedef enum {
 #    if  defined(USE_POSIX_2008_LOCALE)                                     \
      || (defined(WIN32) && (defined(_MSC_VER) || (defined(_UCRT))))
 #      define USE_THREAD_SAFE_LOCALE
+#    else
+#      define EMULATE_THREAD_SAFE_LOCALES
 #    endif
 #  endif